Optical disc recording apparatus and method of forming an image on an optical disc

ABSTRACT

In a case where an image of a density that is uniform over a substantially whole area of an optical disc ( 200 ) is to be formed, a servo circuit ( 138 ) controls the rotation speed of a spindle motor ( 130 ) to be constant, and an ALPC circuit ( 162 ) controls the current level of a drive signal Li so that the laser power is constant. In this case, a main control section ( 170 ) sets the movement distance of an optical pickup ( 100 ) to be larger in the inner peripheral side where the line width of the image is larger, and that of the optical pickup ( 100 ) to be smaller in the outer peripheral side where the line width is smaller. The main control section ( 170 ) sends to a the motor driver ( 142 ) instructions for moving the optical pickup ( 100 ) by a movement distance which is determined on the basis of the setting.

RELATED APPLICATIONS

This application is a divisional application of application Ser. No.10/606,810, filed Jun. 26, 2003.

BACKGROUND OF THE INVENTION

The present invention relates to an optical disc recording apparatuswhich can form an image on an optical disc, and a method of forming animage on an optical disc.

Optical discs such as a CD-R (Compact Disc Recordable) or a CD-RW(Compact Disc Rewritable) are widely used for recording large volumes ofinformation. An optical disc recording apparatus records informationsuch as music data by applying a laser beam to a recording place whichis formed in one face of an optical disc.

An image such as characters indicating a title, symbols, and the like isformed on a label face (opposite to the recording face) of the opticaldisc, thereby enabling data recorded in the recording face to beidentified. Such an image is formed by printing it onto a label sheetwith using a printing apparatus or the like, and then applying the labelsheet to the label face of the optical disc.

Therefore, such a formation of an image on an optical disc requires aprinting apparatus in addition to an optical disc recording apparatus.Furthermore, a troublesome work of applying a label sheet onto which animage is printed to an optical disc is necessary.

In order to solve the problems, an optical disc recording apparatus hasbeen proposed which has a function of forming an image such as titlecharacters on a label face or recording face of an optical disc as shownin FIG. 14 (hereinafter, referred to as drawing function), in additionto a function of recording information such as music data onto theoptical disc (hereinafter, referred to as information recordingfunction).

At present, as an optical disc recording apparatus which can realize thedrawing function, proposed are an optical disc recording apparatus ofthe CLV (Constant Linear Velocity) system in which recording isperformed while controlling the power of a laser beam emitted from anoptical pickup to an optical disc to be constant, and changing therotation number of a spindle motor that rotates the optical disc, andthat of the CAV (Constant Angular Velocity) system in which recording isperformed while controlling the rotation number of a spindle motor to beconstant, and changing the power of a laser beam emitted from an opticalpickup to the optical disc. Such optical disc recording apparatuses havethe following problems.

In an optical disc recording apparatus of the CLV system, as describedabove, an image is formed on an optical disc while changing the rotationnumber of a spindle motor. In the case where address informationspecifying the laser beam irradiation position (i.e., the radialposition of an optical pickup on the optical disc) is previouslyrecorded on the optical disc, the address information can be reproducedso that the radial position of the optical pickup can be determined,thereby enabling a stable rotation control on the spindle motor(hereinafter, referred to as spindle servo).

In the case where address information is not previously recorded on theoptical disc, such as the case where an image is to be formed on thelabel face of the optical disc, however, the radial position of theoptical pickup cannot be determined, with the result that the spindleservo is unstable.

In such a case, the spindle servo is conducted on the basis of an FG(Frequency Generator) signal supplied from a rotation detector attachedto the spindle motor, i.e., a pulse signal in which the pulse generationperiod is changed in accordance with the rotation speed (the rotationnumber per unit time) of the spindle motor. However, the FG signalinvolves a large error, and hence is not suitable for the spindle servoin which the rotation number of the spindle motor is continuouslychanged. The spindle servo affects the writing quality. When the spindleservo is not stabilized, consequently, there arises a problem in thatthe quality of an image to be formed on the optical disc is lowered.

By contrast, in an optical disc recording apparatus of the CAV system,as described above, an image is formed on an optical disc whilemaintaining the rotation number of a spindle motor and changing thelaser power. Therefore, the spindle servo can be performed more stablythan that in the case of an optical disc recording apparatus of the CLVsystem. When the rotation number of the spindle motor is controlled soas to be constant, the linear velocity of the inner peripheral side ofthe optical disc is lower than that of the outer peripheral side. Inorder to form an image of a density which is uniform over asubstantially whole area of the optical disc, therefore, the power of alaser beam irradiated onto the inner peripheral side of the optical discmust be set to be lower than that of a laser beam irradiated onto theouter peripheral side. Namely, the formation of an image of a uniformdensity over a substantially whole area of the optical disc requirescomplex and troublesome works such as that of obtaining an optimum laserpower on the basis of the radial position of the optical pickup.

SUMMARY OF THE INVENTION

The invention has been conducted in view of the above-describedcircumstances. It is an object of the invention to provide an opticaldisc recording apparatus which can form an image of a density that isuniform over a substantially whole area of an optical disc, and a methodof forming an image on an optical disc.

In order to solve the aforesaid object, the invention is characterizedby having the following arrangement.

-   (1) An optical disc recording apparatus comprising:

an optical pickup which applies a laser beam of substantially constantpower to an optical disc;

a rotating section which rotates the optical disc at a substantiallyconstant speed;

a feeding section which moves the optical pickup by a movement distancein a radial direction of the optical disc;

a detecting section which detects a radial position of the opticalpickup with respect to the optical disc; and

a movement distance controlling section which changes the movementdistance set in the feeding section in accordance with the radialposition of the optical pickup detected by the detecting section.

-   (2) The optical disc recording apparatus according to (1), wherein a    rotation number of the optical disc rotated by the rotating section    is controlled by the rotation controlling section to be    substantially constant.-   (3) The optical disc recording apparatus according to (1), wherein    the power of the laser beam is controlled by a laser power    controlling section to be substantially constant.-   (4) The optical disc recording apparatus according to (1), wherein    the feeding section moves the optical pickup each time when the    optical disc is rotated once by the rotating section.-   (5) The optical disc recording apparatus according to (1), wherein    the movement distance controlling section changes the movement    distance set in the feeding section, to be further reduced in a    stepwise manner as the radial position of the optical pickup is    further moved from an inner peripheral side of the optical disc    toward an outer peripheral side.-   (6) The optical disc recording apparatus according to (1) further    comprising a storage section which stores feed management    information for forming an image of a density which is uniform over    a substantially whole area of the optical disc, and for obtaining    the movement distance from the radial position of the optical    pickup,

wherein the movement distance controlling section obtains the movementdistance based on the radial position of the optical pickup that isdetected by said detecting section, and the feed management information.

-   (7) The optical disc recording apparatus according to (1), wherein    the optical disc recording apparatus forms an image on the optical    disc in accordance with image data with using the optical pickup,    the rotating section, the feeding section, the detecting section and    the movement distance controlling section.-   (8) A optical disc recording apparatus comprising:

an optical pickup which applies a laser beam of substantially constantpower to an optical disc;

a rotating section which rotates the optical disc at a substantiallyconstant speed;

a feeding section which, each time when the optical disc is rotated witha number of rotations by the rotating section, moves the optical pickupby a movement distance in a radial direction of the optical disc;

a laser beam irradiation position controlling section which, when theoptical disc is rotated with the preset number of rotations by therotating section, changes an irradiation position of the laser beam sothat the laser beam is moved along a different laser irradiation locuson the optical disc in each rotation;

a detecting section which detects a radial position of the opticalpickup with respect to the optical disc; and

a rotation number controlling section which changes the rotation numberset in the feeding section in accordance with the radial position of theoptical pickup detected by the detecting section.

-   (9) The optical disc recording apparatus according to (8), wherein a    rotation number of the optical disc rotated by the rotating section    is controlled by the rotation controlling section to be    substantially constant.-   (10) The optical disc recording apparatus according to (8), wherein    the power of the laser beam is controlled by a laser power    controlling section to be substantially constant.-   (11) The optical disc recording apparatus according to (8), wherein    the optical disc recording apparatus forms an image on the optical    disc in accordance with image data with using the optical pickup,    the rotating section, the feeding section, the detecting section and    the movement distance controlling section.-   (12) A method of forming an image on an optical disc comprising    steps of:

rotating the optical disc at substantially constant speed;

applying a laser beam of substantially constant power to the opticaldisc by an optical pickup;

moving the optical pickup by a movement distance in a radial directionof the optical disc; and

changing the movement distance in accordance with the radial position ofthe optical pickup on the optical disc.

-   (13) A method of forming an image on an optical disc comprising    steps of:

rotating the optical disc at substantially constant speed;

applying a laser beam of substantially constant power to the opticaldisc by an optical pickup;

moving the optical pickup in a radial direction of the optical disc eachtime when the optical disc is rotated with a number of rotations;

changing an irradiation position of the laser beam so that, when theoptical disc is rotated with the number of rotations, the laser beam ismoved along a different laser irradiation locus on the optical disc ineach rotation; and

changing the number of rotations in accordance with the radial inaccordance with the radial position of the optical pickup on the opticaldisc.

-   (14) An optical disc including a heat-sensitive layer in which an    image is formed by discoloring the heat-sensitive layer, the image    being formed by the steps of:

rotating the optical disc at substantially constant speed;

applying a laser beam of substantially constant power to the opticaldisc by an optical pickup;

moving the optical pickup by a movement distance in a radial directionof the optical disc;

changing the movement distance in accordance with the radial position ofthe optical pickup on the optical disc.

-   (15) An optical disc including a heat-sensitive layer in which an    image is formed by discoloring the heat-sensitive layer, the image    being formed by the steps of:

rotating the optical disc at substantially constant speed;

applying a laser beam of substantially constant power to the opticaldisc by an optical pickup;

moving the optical pickup in a radial direction of the optical disc eachtime when the optical disc is rotated with a number of rotations;

changing an irradiation position of the laser beam so that, when theoptical disc is rotated with the number of rotations, the laser beam ismoved along a different laser irradiation locus on the optical disc ineach rotation; and

changing the number of rotations in accordance with the radial inaccordance with the radial position of the optical pickup on the opticaldisc.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing the configuration of main portions ofan optical disc recording apparatus of a first embodiment.

FIG. 2 is a timing chart showing an FG signal, a clock signal Dck, and areference signal SFG in the embodiment.

FIG. 3 is a diagram illustrating an image formation format of an opticaldisc in the embodiment.

FIG. 4 is a block diagram illustrating the function of a main controlsection in the embodiment.

FIG. 5 is a view showing an example of a feed management table in theembodiment.

FIG. 6A is a partial enlarged view schematically showing an optical discon which an image is formed, and FIG. 6B is a diagram illustrating laserirradiation loci.

FIG. 7 is a diagram showing an example of stored contents of a framememory in the embodiment.

FIG. 8 is a flowchart illustrating an image forming process in theembodiment.

FIG. 9 is a diagram showing the configuration of main portions of anoptical disc recording apparatus of a second embodiment.

FIG. 10 is a block diagram illustrating the function of a main controlsection in the embodiment.

FIG. 11 is a view showing an example of a rotation number managementtable in the embodiment.

FIG. 12 is a view showing examples of laser irradiation loci of rows inthe embodiment.

FIG. 13 is a flowchart illustrating an image forming process in theembodiment.

FIG. 14 is a view showing an example of an image formed on an opticaldisc.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Hereinafter, embodiments in which the invention is applied to an opticaldisc recording apparatus having the drawing function will be described.The optical disc recording apparatus of each of the embodiments realizesformation of an image of a density that is uniform over a substantiallywhole area of an optical disc in a state where the rotation number of aspindle motor and the laser power are controlled so as to be constant.

A. First Embodiment

(1) Configuration of the Embodiment

FIG. 1 is a block diagram showing the configuration of main portions ofan optical disc recording apparatus 10 of a first embodiment.

The optical disc recording apparatus 10 of the embodiment has thedrawing function, and also the information recording function which isidentical with that of a conventional optical disc recording apparatus.In addition to the various components shown in FIG. 1, therefore, othercomponents (for example, an RF amplifier, a decoder, and a strategycircuit) which are similar to those mounted on a conventional opticaldisc recording apparatus are mounted on the optical disc recordingapparatus 10. In order to facilitate the understanding of the invention,illustration and description of such components are omitted.

An optical disc 200 is a disc-shape recording medium such as a CD-R or aCD-RW, and has a recording face on which music data or like informationcan be recorded, and a label face on which an image can be formed. Whenan image is to be formed on the optical disc 200, the disc is set sothat the label face is opposed to an optical pickup 100, and the opticalpickup 100 irradiates a laser beam of a constant strength onto the labelface to form a desired image. Although a case where an image is formedon the label face of the optical disc 200 will be described, an imagemay be formed on the recording face by, for example, using a blank areaof the recording face.

A spindle motor 130 is a section which rotates the optical disc 200.Based on a control signal SS supplied from a servo circuit 138, thespindle motor rotates the optical disc 200.

A rotation detector 132 is a section which detects the rotation speed ofthe spindle motor 130, and, while using the counter electromotive forceof the spindle motor 130, supplies an FG signal of a frequencycorresponding to the rotation speed of the spindle motor 130, to theservo circuit 138.

Under the control by a main control section 170, the servo circuit 138generates the control signal SS on the basis of the FG signal suppliedfrom the rotation detector 132, and supplies the control signal to thespindle motor 130, thereby implementing the spindle servo. The servocircuit 138 conducts other servo controls including a focusing servocontrol (a servo control for focusing the laser beam) on the opticalpickup 100, and a tracking servo control (a servo control for tracing atrack where pits are formed), in addition to the spindle servo. In theembodiment, as described above, an image is formed on the optical disc200 while controlling the rotation number of the spindle motor 130 so asto be constant. When an image is to be formed on the optical disc 200,therefore, the servo circuit 138 receives instructions for controllingthe rotation number so as to be constant, from the main control section170, and in accordance with the instructions implements the spindleservo so that the rotation number of the spindle motor 130 obtained fromthe FG signal is constant.

The optical pickup 100 comprises a laser diode, a four-splitphotodetector, and an objective lens actuator (which are not shown), andapplies the laser beam to the optical disc 200 to record music data orthe like and form an image such as title characters.

A stepping motor 140 moves the optical pickup 100 in a radial directionof the optical disc 200 in accordance with a motor drive signal MSsupplied from a motor driver 142.

According to instructions from the main control section 170, the motordriver 142 generates the motor drive signal MS for moving the opticalpickup 100 in the instructed direction and by the instructed movementdistance, and supplies the signal to the stepping motor 140.

A PLL circuit 144 generates a clock signal Dck which is synchronizedwith the FG signal supplied from the rotation detector 132, and in whichthe frequency is a multiple of the frequency of the FG signal, andsupplies the clock signal to the main control section 170.

A frequency divider 146 generates a reference signal SFG which isobtained by dividing the frequency of the FG signal supplied from therotation detector 132 with a constant number, and supplies the referencesignal to the main control section 170.

FIG. 2 is a timing chart showing the FG signal, the clock signal Dck,and the reference signal SFG which are generated in the rotationdetector 132, the PLL circuit 144, and the frequency divider 146,respectively, and FIG. 3 is a diagram illustrating the image formationformat of the optical disc 200. In FIG. 3, for the sake of convenience,loci of movement in which the optical pickup 100 is moved for eachrotation of the optical disc are defined as a 1st row, a 2nd row, a 3rdrow, . . . , an m-th row (the last row) as advancing from the innerperipheral side to the outer peripheral side. One of radials is set as areference line, and other radials are defined as a 1st column, a 2ndcolumn, a 3rd column, . . . , an n-th column (the last column) asadvancing in a clockwise direction. In FIG. 3, the widths of the rows,i.e., movement distances p₁, . . . , p_(m-1) of the optical pickup 100in respective rotations of the optical disc are different from oneanother. The reason of this configuration will be described later.

As shown in FIG. 2, during a period when the spindle motor 130 makes onerotation (i.e., when the optical disc 200 makes one rotation), therotation detector 132 generates a k number of pulses as the FG signal.In this case, the frequency divider 146 divides the frequency of the FGsignal by k, and supplies the frequency-divided signal to the maincontrol section 170 as the reference signal SFG. The main controlsection 170 detects rising timings and the number of risings in thereference signal SFG to detect the rotation timings (the timings whenthe laser beam irradiation position passes the reference line shown inFIG. 3) and rotation number of the optical disc 200.

By contrast, the PLL circuit 144 supplies the clock signal Dck which isobtained by multiplying the frequency of the FG signal by n/k, to themain control section 170. The one period of the clock signal Dckcoincides with the period when the optical disc 200 is rotated by anangle corresponding to one column shown in FIG. 3. When the main controlsection 170 detects rising timings and the number of risings in theclock signal Dck, therefore, the main control section can detect thecolumn of the optical disc 200 where the laser beam irradiation positionof the optical pickup 100 exists. It is a matter of course that, inplace of the rising timings of the reference signal SFG, other timingssuch as falling timings can be used, and, in place of the rising timingsof the clock signal Dck, other timings such as falling timings can beused.

More exactly speaking, the reference line of the optical disc 200 shouldbe the reference line with respect to the rotation shaft of the spindlemotor 130. In an image forming process or the like, the optical disc 200is rotated under the state where the disc is chucked to a table (notshown) which is directly coupled to the rotation shaft. Therefore, thereference line with respect to the rotation shaft of the spindle motor130 maintains a fixed positional relationship with a certain one ofradials of the optical disc 200. As far as the state is maintained,consequently, one radial of the optical disc 200 can be called thereference line of the optical disc 200.

Referring back to FIG. 1, the main control section 170 is configured bya CPU, a ROM, a RAM, and the like, and implements various controlprograms stored in the ROM to control various portions of the opticaldisc recording apparatus 10, and control also the movement distance ofthe optical pickup 100 for each rotation of the optical disc.

FIG. 4 is a block diagram illustrating the function of the main controlsection 170.

A radial position detecting section 171 detects rising timings of thereference signal SFG supplied from the frequency divider 146, risingtimings of the clock signal Dck supplied from the PLL circuit 144, andthe like, to know the row and column of the optical disc 200 where theoptical pickup 100 is positioned, i.e., the radial position of theoptical pickup 100.

More specifically, each time when a rise of the reference signal SFG isdetected, the radial position detecting section 171 increments by “1”the count value of a row number counter 171 a which is used for knowingthe row where the optical pickup 100 is positioned. Each time when arise of the clock signal Dck is detected, the radial position detectingsection 171 increments by “1” the count value of a column number counter171 b which is used for knowing the column where the optical pickup 100is positioned. The radial position detecting section 171 obtains theradial position of the optical pickup 100 from the count values of therow number counter 171 a and the column number counter 171 b.

A movement distance controlling section 172 determines the movementdistance of the optical pickup 100 for each rotation of the opticaldisc. The movement distance of the optical pickup 100 is obtained on thebasis of the radial position of the optical pickup 100 which is detectedby the radial position detecting section 171, and a feed managementtable TA (see FIG. 5) which is stored in a storage section 173.

FIG. 5 is a view showing an example of the feed management table TA.

In the feed management table TA, radial positions of the optical pickup100 and movement distances of the optical pickup 100 are correspondinglyregistered. As shown in FIG. 5, the movement distance of the opticalpickup 100 is set so as to be further reduced in a stepwise manner asthe radial position is further moved from the inner peripheral sidetoward the outer peripheral side. The reason of such setting will bedescribed with reference to FIG. 6.

FIG. 6A is a partial enlarged view schematically showing the opticaldisc 200 on which an image is formed, and FIG. 6B is a diagramillustrating laser irradiation loci on the optical disc 200. Inpractice, laser irradiation loci are arcuate. In FIG. 6B, for the sakeof convenience, however, they are shown in a linearly developed manner.

As described above, in the embodiment, a desired image is formed on theoptical disc 200 in the state where not only the rotation number of thespindle motor 130 but also the laser power are controlled so as to beconstant. When a laser beam is applied at the same power and for thesame time period onto an area in the inner peripheral side (for example,the 1st row) of the optical disc 200 and that in the outer peripheralside (for example, the m-th row), a line width W₁ of the image which isformed in the 1st row is larger than a line width W_(m) of the imagewhich is formed in the m-th row (see FIG. 6A). Namely, a line width ofan image which is formed in the inner peripheral side (hereinafter,referred to as an inner-peripheral side image) is larger than that of animage which is formed in the outer peripheral side (hereinafter,referred to as an outer-peripheral side image). As a result, the densityof the inner-peripheral side image is higher than that of theouter-peripheral side image. When no countermeasure is taken, therefore,it is impossible to attain the object of the invention that “an image ofa density that is uniform over a substantially whole area of an opticaldisc is formed.”

In the embodiment, therefore, the movement distance of the opticalpickup 100 is determined in accordance with the line width as shown inFIG. 6B. Specifically, the movement distance is set larger in the innerperipheral side where the line width is larger, and set smaller in theouter inner peripheral side where the line width is smaller. When themovement distance of the optical pickup 100 is set in this way, an imageof a density that is uniform over a substantially whole area of theoptical disc 200 can be formed even in the state where not only therotation number of the spindle motor 130 but also the laser power arecontrolled so as to be constant.

Referring again to FIG. 1, an ALPC (Automatic Laser Power Control)circuit 162 controls the power of the laser beam irradiated by theoptical pickup 100. The ALPC circuit 162 controls the current level of adrive signal Li so that the light intensity of the laser beam emittedfrom the optical pickup 100 coincides with the target value of theoptimum laser power which is instructed by the main control section 170.In the embodiment, as described above, an image is formed on the opticaldisc 200 while controlling the laser power so as to be constant. When animage is to be formed on the optical disc 200, therefore, the ALPCcircuit 162 receives instructions for controlling the laser power so asto be constant, from the main control section 170, and in accordancewith the instructions controls the optical pickup so that the laserpower is constant. In the invention, “the laser power is controlled soas to be constant” means that each of the write and bottom levels of thelaser intensity which will be described later is controlled so as to beconstant irrespective of the radial position of the optical pickup 100.

A frame memory 158 stores information which is supplied from a hostcomputer via an interface 150, i.e., information relating to an imagewhich is to be formed on the optical disc 200 (hereinafter, suchinformation is referred to as image data). The image data is used forspecifying image forming positions and non-image forming positions inthe optical disc 200, and stored into the frame memory 158 in anarrangement of m rows and n columns.

FIG. 7 is a diagram showing an example of the stored contents of theframe memory 158.

As shown in the figure, ON data indicating that the laser strength isset to the write level (a laser intensity which is sufficient fordiscoloring a heat-sensitive layer of the optical disc 200) is stored atmatrix elements corresponding to image forming positions, and OFF dataindicating that the laser strength is set to the bottom level (a laserintensity by which the heat-sensitive layer of the optical disc 200 isnot discolored) is stored at matrix elements corresponding to non-imageforming positions.

Referring back to FIG. 1, the image data stored in the frame memory 158are sequentially transferred to a laser driver 164 under the control ofthe main control section 170. The laser driver 164 generates the drivesignal Li in which the control contents of the ALPC circuit 162 arereflected, in accordance with the image data which are sequentiallytransferred from the frame memory 158, and supplies the drive signal tothe optical pickup 100. The intensity of the laser beam emitted from theoptical pickup 100 is feedback-controlled so as to coincide with thetarget value supplied from the main control section 170.

In the above, the configuration of the optical disc recording apparatus10 of the embodiment has been described in detail. Hereinafter, anoperation in the case where a desired image is to be formed on the labelface of the optical disc 200 with using the optical disc recordingapparatus 10 will be described.

-   (2) Operation of the Embodiment

FIG. 8 is a flowchart illustrating an image forming process which isimplemented in the image formation by the main control section 170 ofthe optical disc recording apparatus 10.

When a desired image is to be formed on the optical disc 200, the userfirst sets the optical disc 200 so that the label face of the opticaldisc 200 is opposed to the optical pickup 100. The user then operatesthe host computer and the like to select image data corresponding to theimage to be formed, and inputs instructions for starting the imageformation (hereinafter, referred to as image formation instructions).

When the image data is selected, the selected image data is suppliedfrom the host computer to the optical pickup 100 via the interface 150,and then stored into the frame memory 158 (see FIG. 7).

Upon receiving the image formation instructions, the main controlsection 170 sends to the servo circuit 138 instructions for controllingthe rotation number (rotation speed) of the spindle motor 130 so as tobe constant, and to the ALPC circuit 162 instructions for controllingthe laser power so as to be constant (step S1). In accordance with theinstructions sent from the main control section 170, the servo circuit138 executes the spindle servo so that the rotation speed of the spindlemotor 130 is constant. On the other hand, in accordance with theinstructions sent from the main control section 170, the ALPC circuit162 controls the current level of the drive signal Li so that the laserpower is constant.

After the main control section 170 sends the instructions to the servocircuit 138 and the ALPC circuit 162, the main control section sends tothe motor driver 142 instructions for moving the optical pickup 100 to aposition corresponding to the innermost periphery (the 1st row) of theoptical disc 200 (step S2). In accordance with the instructions, themotor driver 142 generates the motor drive signal MS which is requiredfor moving the optical pickup 100 to the position. The stepping motor140 is rotated according to the motor drive signal MS supplied from themotor driver 142, with the result that the optical pickup 100 is movedto the position.

Next, the main control section 170 starts detection of rising timings ofthe reference signal SFG and the clock signal Dck. When a rise of thereference signal SFG is detected, the main control section 170 sets thecount value x (1≦x≦m) of the row number counter 171 a to “1” (step S3).When a rise of the clock signal Dck is detected, the main controlsection 170 sets the count value y (1≦y≦n) of the column number counter171 b to “1” (step S4).

Then, the main control section 170 reads out the image data of thematrix element corresponding to the count values (in this case, 1st rowand 1st column) from the frame memory 158 (see FIG. 7), and transfersthe image data to the laser driver 164. In the case where thetransferred image data is ON data, the laser driver 164 generates thedrive signal Li corresponding to the write level, and supplies thegenerated drive signal to the optical pickup 100. In accordance with thedrive signal Li, the optical pickup 100 applies a laser beam of thewrite level to the optical disc 200, with the result that theheat-sensitive layer of a portion corresponding to the matrix element isdiscolored.

By contrast, in the case where the transferred image data is OFF data,the laser driver 164 generates the drive signal Li corresponding to thebottom level, and supplies the generated drive signal to the opticalpickup 100. In accordance with the drive signal Li, the optical pickup100 applies a laser beam of the bottom level to the optical disc 200,with the result that the heat-sensitive layer of a portion correspondingto the matrix element is not discolored.

Thereafter, the main control section 170 judges whether the count valuey of the column number counter 171 b reaches “n” or not, i.e., whetherimage data of the last column is processed or not (step S6). If it isjudged that the count value y of the column number counter does notreach “n” (step S6: NO), the main control section 170 increments by “1”the count value of the column number counter 171 b (step S7), and thecontrol returns to step S5. A series of processes which are to beconducted after returning to step S5 are conducted in synchronizationwith one period of the clock signal Dck, and hence the image formationis performed on each column.

If, during repetition of the above-mentioned process, the main controlsection 170 detects in step S6 that the count value y of the columnnumber counter 171 b reaches “n” (step S6: YES), the control proceeds tostep S8. Then, the main control section 170 judges whether the countvalue x of the row number counter 171 a reaches “m” or not, i.e.,whether image data of the last row is processed or not. If it is judgedthat the count value x of the row number counter 171 a does not reach“m” (step S8: NO), the main control section 170 determines the movementdistance of the optical pickup 100 from the feed management table TAshown in FIG. 5 and the radial position of the optical pickup 100 atthis timing (step S9).

In the case where the radial position of the optical pickup 100 at thistiming is 1st row and n-th column, for example, the main control section170 conducts a search on the feed management table TA while using theradial position as a search key, thereby obtaining a movement distancep₁ which has a larger value. By contrast, in the case where the radialposition of the optical pickup 100 at this timing is (m−1)th row andn-th column, the main control section 170 conducts a search on the feedmanagement table TA while using the radial position as a search key,thereby obtaining a movement distance p_(m-1) which has a smaller value.In this way, in the inner peripheral side of the optical disc 200 wherethe line width is larger, the movement distance is set larger, and, inthe outer peripheral side of the optical disc 200 where the line widthis smaller, the movement distance is set smaller, so that, even in astate where the rotation number of the spindle motor 130 and the laserpower are controlled so as to be constant, an image of a density that isuniform over a substantially whole area of the optical disc 200 can beformed (the detail of the formation has been described in the paragraphof Configuration of the embodiment).

When the movement distance of the optical pickup 100 is determined asdescribed above, the main control section 170 gives to the motor driver142 instructions for moving the optical pickup 100 to a position whichis separated by a distance corresponding to the movement distance towardthe outer peripheral side. In accordance with the instructions, themotor driver 142 generates the motor drive signal MS which is requiredfor moving the optical pickup 100 to the position. The stepping motor140 is rotated in accordance with the motor drive signal MS suppliedfrom the motor driver 142, with the result that the optical pickup 100is moved to the position.

After giving the instructions, the main control section 170 incrementsby “1” the count value x of the row number counter 171 a (step S10), andthe control returns to step S4. A series of processes which are to beconducted after returning to step S4 are conducted in synchronizationwith one period of the reference signal SFG, and hence the imageformation is performed on each row.

If, during repetition of the above-mentioned process, it is detected instep S8 that the count value x of the row number counter 171 a reaches“m” (step S8: YES), the main control section 170 judges that the imageformation on the optical disc 200 is completed, and ends the imageforming process which has been described above.

As described above, according to the optical disc recording apparatus 10of the embodiment, in the inner peripheral side where the line width islarger when a laser beam of the same power is applied, the movementdistance of the optical pickup 100 is set larger, and, in the outerperipheral side where the line width is smaller, the movement distanceof the optical pickup 100 is set smaller. When the movement distance ofthe optical pickup 100 is set in accordance with the line width of animage formed on the optical disc 200 in this way, an image of a densitythat is uniform over a substantially whole area of the optical disc 200can be formed even in a state where the rotation number of the steppingmotor 140 and the laser power are controlled so as to be constant.

-   (3) Modifications

The invention is not restricted to the embodiment described above, andcan be modified in the following exemplary manners.

<Modification 1>

In the embodiment described above, the main control section 170 detectsrising timings and the number of risings in the reference signal SFG andthe clock signal Dck, to determine the radial position of the opticalpickup 100. In the case where an image is to be formed in a blank areain a recording face in which address information is recorded, forexample, the radial position of the optical pickup 100 may be determinedby reproducing the address information which is obtained from theoptical pickup 100 via the RF amplifier and the decoder (which are notshown).

<Modification 2>

In the embodiment described above, the main control section 170determines the movement distance of the optical pickup 100 on the basisof the radial position of the optical pickup 100 and the feed managementtable TA. Alternatively, for example, a movement distance calculationalgorithm (a function or the like) which can uniquely determine themovement distance from the radial position may be stored in the storagesection 173, and the radial position may be substituted into themovement distance calculation algorithm to determine the movementdistance. Namely, the feed management information set forth in theappended claims means any kind of information in which the movementdistance of the optical pickup 100 can be obtained from the radialposition of the optical pickup 100.

B. Second Embodiment

(1) Configuration of the Embodiment

In the first embodiment described above, the movement distance of theoptical pickup 100 is adequately set in accordance with the line widthof an image to be formed on the optical disc 200, thereby forming animage of a density that is uniform over a substantially whole area ofthe optical disc 200.

By contrast, in the second embodiment, the number of overwritings(described later) of an image to be formed on the optical disc 200 isadequately set in accordance with the line width of the image, wherebyan image of a density that is uniform over a substantially whole area ofthe optical disc 200 is formed.

FIG. 9 is a diagram showing the configuration of main portions of anoptical disc recording apparatus 20 of the embodiment. In the followingdescription, portions corresponding to those of the optical discrecording apparatus 10 of the first embodiment are denoted by the samereference numerals, and their description is omitted.

As well known in the art, in a conventional optical disc recordingapparatus, when various information (such as music data) is to berecorded onto the optical disc 200, the servo circuit 138 generates atracking signal which is used for eliminating a deviation of a spotposition of the laser beam emitted from the optical pickup 100 from thecenter position of a guide groove formed in the optical disc 200, anddrives a tracking actuator 122 in accordance with instructions givenfrom the main control section 170, whereby correct tracking is realized.

By contrast, in the optical disc recording apparatus 20 of theembodiment, when an image is to be formed on the optical disc 200, theservo circuit 138 generates a tracking signal Tr (for example, atriangular signal) for image formation which will be described later,and drives the tracking actuator 122 in accordance with instructionsgiven from the main control section 170, whereby tracking forcontrolling the laser beam irradiation position on the optical disc 200is realized. In the following description, in order to avoid confusionin understanding, a tracking control which is performed in informationrecording is referred to as a usual tracking control, and a trackingcontrol which is performed in image formation is referred to as an imageformation tracking control.

FIG. 10 is a block diagram illustrating the function of the main controlsection 170 in the embodiment.

A radial position detecting section 271 includes a rotation numbercounter 271 a for obtaining the number of rotations of the optical disc200, and the row and column number counters 171 a and 171 b which havebeen described in the first embodiment. Each time when a rising timingof the reference signal SFG supplied from the frequency divider 146 isdetected, the radial position detecting section 271 increments by “1”the count value of the rotation number counter 271 a. The radialposition detecting section 271 conducts a search on a rotation numbermanagement table TB (see FIG. 11) while using the count value of therotation number counter 271 a as a search key.

The radial position detecting section 271 conducts such a search to knowthe radial position (the number of rows) of the optical pickup 100 andthe number of rotations along the row at the present timing (this willbe described later). Based on the result of the search, the radialposition detecting section 271 increments the count value of therotation number counter 271 a, and also that of the row number counter171 a. Each time when a rising timing of the clock signal Dck suppliedfrom the PLL circuit 144 is detected, the radial position detectingsection 271 increments by “1” the count value of the column numbercounter 171 b, to know the radial position (the number of columns) ofthe optical pickup 100 at the present timing.

FIG. 11 is a view showing an example of the rotation number managementtable TB stored in a storage section 272.

In the rotation number management table TB, the radial position (thenumber of rows) of the optical pickup 100 and the number of rotations atwhich the optical disc 200 is to be rotated are correspondinglyregistered. The rotation numbers of the optical disc 200 for respectiverows are different from one another, and set so as to be furtherincreased in a stepwise manner as the radial position is further movedfrom the inner peripheral side toward the outer peripheral side.

By conducting a search on the rotation number management table TB whileusing the count value of the rotation number counter 271 a as a searchkey, the radial position detecting section 271 knows the radial position(the number of rows) of the optical pickup 100 and the number ofrotations along the row at the present timing. In the case where thecount value is “3”, for example, the radial position detecting section271 determines that the radial position (the number of rows) of theoptical pickup 100 is the 2nd row, and the pickup makes two rotationsalong the 2nd row.

As described above, different rotation numbers for the respective rowsare registered in the rotation number management table TB. The reason ofthis setting will be described. When a laser beam is applied at the samepower and for the same time period in a state where the rotation numberof the spindle motor 130 is controlled so as to be constant, the linewidth of inner-peripheral side image is larger than that of anouter-peripheral side image, with the result that the inner-peripheralside image is higher in density than the outer-peripheral side image.Therefore, an image is formed by applying the laser beam to the opticaldisc 200 in each rotation while the rotation number is set to a smallervalue in the inner peripheral side where the line width is larger, andthe rotation number is set to a larger value in the outer peripheralside where the line width is smaller.

However, when the laser beam is simply applied in each rotation, thelaser beam irradiation position is moved along the same locus in pluralrotations. In the embodiment, therefore, the tracking signal Tr forimage formation is supplied in each rotation while setting only thephase of the signal to have a different value for each rotation, so thatdifferent laser irradiation loci are formed. An example of this will bedescribed. The timing when the laser beam irradiation position passesthe reference line is set as zero in the time axis. In the case wherethe optical disc 200 is rotated seven times in order to form an image ofone row, the main control section 170 gives to the servo circuit 138instructions for generating triangular signals as the image formationtracking signal Tr. In the triangular signal for the first rotation, thephase is set to zero, and, in the triangular signals for the second andsubsequent rotations, the phase is sequentially delayed by 2π/7. As aresult, it is possible to form an image of a density which is uniformover a substantially whole area of the optical disc 200. The laserirradiation loci will be described in detail later.

Referring back to FIG. 10, when the radial position detecting section271 knows the radial position (the number of rows) of the optical pickup100 and the number of rotations along the row as described above, thesection notifies a laser beam irradiation position controlling section273 of this knowing.

Upon reception of the notification, the laser beam irradiation positioncontrolling section 273 gives to the servo circuit 138 instructions forgenerating the image formation tracking signal Tr in which only thephase is made different for each rotation as described above. Inaccordance with the instructions, the servo circuit 138 generates theimage formation tracking signal Tr in which only the phase is madedifferent for each rotation, and supplies the signal to the trackingactuator 122, whereby the image formation tracking control is conductedin place of the usual tracking control. In the generation of the imageformation tracking signal Tr, the manner of determining the variationamount of the phase can be suitably changed in accordance with, forexample, the design of the optical disc recording apparatus 20.

FIG. 12 is a view showing examples of laser irradiation loci of rows inthe case where triangular signals are sequentially supplied as the imageformation tracking signal Tr to the tracking actuator 122. In practice,laser irradiation loci are arcuate. In FIG. 12, for the sake ofconvenience, however, they are shown in a linearly developed manner.FIG. 12 shows the case where the optical disc 200 is rotated one time toform an image of the 1st row, rotated two times to form an image of the2nd row, . . . , and rotated m times to form an image of the m-th row.

In the embodiment, when an image of one row is to be formed, the laserbeam is irradiated onto the optical disc 200 by the number of rotationscorresponding to the row, thereby discoloring the heat-sensitive layer.When an image of the 1st row is to be formed, therefore, the laser beamis irradiated only one time onto the optical disc 200. When an image ofthe 2nd row is to be formed, the laser beam is irradiated only two timesonto the optical disc 200. When an image of the m-th row to be formed,the laser beam is irradiated m times onto the optical disc 200 (see FIG.12). As shown in the figure, in the 2nd and subsequent rows in which thedisc is rotated plural times, the laser irradiation loci in respectiverotations are different from one other. In the following description, anoperation of forming an image by irradiating the laser beam plural timesalong the same row is often called overwriting.

As described above, according to the embodiment, in the inner peripheralside where the line width is larger (see the line width W₁ shown in FIG.12), the rotation number is set to a smaller value so as to reduce thenumber of overwritings, and, in the outer peripheral side where the linewidth is smaller (see the line width W_(m) shown in FIG. 12), therotation number is set to a larger value so as to increase the number ofoverwritings. As a result, it is possible to form an image of a densitywhich is uniform over a substantially whole area of the optical disc200.

The main portions of the optical disc recording apparatus 20 of theembodiment are configured as described above. Hereinafter, an operationin the case where a desired image is formed on the label face of theoptical disc 200 with using the optical disc recording apparatus 20 willbe described.

(2) Operation of the Embodiment

FIG. 13 is a flowchart illustrating an image forming process which isimplemented in the image formation by the main control section 170 ofthe optical disc recording apparatus 20. Steps in FIG. 13 whichcorrespond to those in FIG. 8 described above are denoted by the samereference numerals, and their description is omitted. The operationswhich are to be conducted by the user to select image data correspondingto the image to be formed, and input image formation instructions areidentical with those in the first embodiment, and hence theirdescription is omitted.

In the main control section 170, the control proceeds from step S1 tostep S2. When a rise of the reference signal SFG is detected, the countvalue x (1≦x≦m) of the row number counter 171 a is set to “1” (step S3).Then, the main control section 170 sets the count value z of therotation number counter 271 a to “1”. When a rise of the clock signalDck is detected, the count value y (1≦y≦n) of the column number counter171 b is set to “1” (step S3 a→step S4).

The main control section 170 refers the count value x of the row numbercounter 171 a, and the count value z of the rotation number counter 271a, and sends to the servo circuit 138 instructions for generating theimage formation tracking signal Tr at the phase which is attained by a znumber of rotations along the x-th row (for example, the phase which isobtained when one rotation is made along the 1st row) (step S4 a). Then,the main control section 170 reads out the image data of the matrixelement corresponding to the count values from the frame memory 158 (seeFIG. 7), and transfers the image data to the laser driver 164 (step S5).

The servo circuit 138 generates the image formation tracking signal Trin accordance with the instructions given from the main control section170, and the laser driver 164 generates the drive signal Li inaccordance with the transferred image data. The signals are supplied tothe optical pickup 100. As a result, the laser beam emitted from theoptical pickup 100 follows the locus in the case of a z number ofrotations along the n-th row, among the loci shown in FIG. 12.

Thereafter, the main control section 170 judges whether the count valuey of the column number counter 171 b reaches “n” or not, i.e., whetherimage data of the last column is processed or not (step S6). If it isjudged that the count value y of the column number counter does notreach “n” (step S6: NO), the main control section 170 increments by “1”the count value of the column number counter 171 b (step S7), and thecontrol returns to step S4 a. The series of processes which have beendescribed above are repeatedly conducted, so that an image of onerotation is formed in the corresponding row.

If, during repetition of the above-mentioned series of processes, themain control section 170 detects in step S6 that the count value y ofthe column number counter 171 b reaches “n” (step S6: YES), the controlproceeds to step S8. Then, the main control section 170 judges whetherthe count value x of the row number counter 171 a reaches “m” or not,i.e., whether image data of the last row is processed or not. If it isjudged that the count value x of the row number counter 171 a does notreach “m” (step S8: NO), the main control section 170 conducts a searchon the rotation number management table TB while using the count value zof the rotation number counter 271 a and the count value of the rownumber counter 171 a as search keys, to judge whether the count valuereaches the rotation number of the corresponding row or not (step S8 a).

In the case where, at this timing, the count value z of the rotationnumber counter 271 a is “1” and the count value x of the row numbercounter 171 a is “2”, for example, the main control section 170 judgesthat the count value does not reach the rotation number of thecorresponding row (step S8: NO) because “2” is registered as therotation number of the 2nd row in the rotation number management tableTB, and the control proceeds to step S8 d. In step S8 d, the maincontrol section 170 increments by “1” the count value z of the rotationnumber counter, and the control returns to step S4. When the series ofprocesses which have been described above are repeatedly conducted, animage of rotations the number of which is defined in the correspondingrow is formed.

By contrast, in the case where, at this timing, the count value z of therotation number counter 271 a is “2” and the count value x of the rownumber counter 171 a is “2”, the main control section 170 judges thatthe count value reaches the rotation number of the corresponding row(step S8: YES) because “2” is registered as the rotation number of the2nd row in the rotation number management table TB, and the controlproceeds to step S8 b. In step S8 b, the main control section 170 resetsthe count value z of the rotation number counter 271 a, and thenincrements by “1” the count value x of the row number counter 171 a(step S8 c). Thereafter, the control returns to step S3 a. When theseries of processes which have been described above are repeatedlyconducted, images over the innermost peripheral row of to the outermostperipheral row are formed.

If, during repetition of the above-mentioned processes, the main controlsection 170 detects in step S8 a that the count value x of the rownumber counter 171 a reaches “m” (step S8: YES), the section judges thatthe image formation on the optical disc 200 is completed, and theabove-described image forming process is ended.

As described above, according to the optical disc recording apparatus 20of the embodiment, in the inner peripheral side where the line width islarger, the rotation number is set to a smaller value and the number ofoverwritings is reduced, and, in the outer peripheral side where theline width is smaller, the rotation number is set to a larger value andthe number of overwritings is increased. In this way, the rotationnumber in each row is set in accordance with the line width of an imageto be formed on the optical disc 200, whereby an image of a density thatis uniform over a substantially whole area of the optical disc 200 canbe formed even in a state where the rotation number of the steppingmotor 140 and the laser power are controlled so as to be constant.

(3) Modifications

The invention is not restricted to the embodiment described above, andcan be modified in the following exemplary manners.

<Modification 1>

In the embodiment described above, a triangular signal is exemplarilyused as the image formation tracking signal Tr. Alternatively, a DCvoltage signal may be used. In the case where a DC voltage signal isused as the image formation tracking signal Tr, the voltage can be setto be different for each rotation. However, the displacement amount dueto a DC voltage signal (i.e., the degree of a change which is caused byan application of a certain voltage) is not clearly known unless it ispreviously obtained by experiments or the like. In a configuration wherea DC voltage is applied, moreover, there is a high possibility that animage is ununiformly formed because of generation of noises, dispersionof sensitivity, etc. Therefore, preferably, an AC signal such as theabove-mentioned triangular signal or a sinusoidal signal is used as theimage formation tracking signal Tr, and the signal is set so as to havea different phase for each rotation.

<Modification 2>

The first embodiment may be applied to the above-described embodiment.Specifically, the movement distance of the optical pickup 100 in theinner peripheral side is made different from that in the outerperipheral side, and also the rotation number (the number ofoverwritings) in each row in the inner peripheral side is made differentfrom that in the outer peripheral side. In this way, the technicalconcept of “an image of a density that is uniform over a substantiallywhole area of the optical disc 200 is formed by changing the movementdistance of the optical pickup 100,” and that of “an image of a densitythat is uniform over a substantially whole area of the optical disc 200is formed by changing the number of overwritings in each row” may beadequately combinedly used. It is a matter of course that any of themodifications of the first embodiment can be applied to theabove-described embodiment.

<Modification 3>

Although the embodiments which use a CD-R or a CD-RW have beendescribed, the invention can be applied to an optical disc of any kind,such as a DVD-R (Digital Versatile Disc Recordable) or a DVD-RAM(Digital Versatile Disc Random Access Memory). The drawing function (theimage forming process and the like) which is realized by the opticaldisc recording apparatus 10 or 20 may be realized by software.Specifically, such software is installed on the optical disc recordingapparatus 10 or 20 from a recording medium (for example, a CD-R) onwhich the software is recorded, or the software is downloaded from aserver having the software via a network (e.g., the Internet), and theninstalled on the optical disc recording apparatus 10 or 20 via apersonal computer or the like. In this way, the above-described variousfunctions can be realized by software.

As described above, according to the invention, an image of a densitythat is uniform over a substantially whole area of an optical disc canbe formed even in a state where the rotation number of a stepping motorand a laser power are controlled so as to be constant.

1. An optical disc recording apparatus for forming an image on anoptical disc, the apparatus comprising: an optical pickup which appliesa laser beam of substantially constant power to the optical disc; arotating section which rotates the optical disc at a substantiallyconstant speed; a storage section storing a table including radialpositions of the optical pickup and a number of rotations the opticaldisk is to be rotated corresponding to each of the radial positions ofthe optical pickup, wherein the number of rotations the optical disk isto be rotated is different for each of the radial positions; a detectingsection which detects a first radial position of the optical pickup withrespect to the optical disc; a feeding section which, when the opticaldisc has been rotated the number of rotations by the rotating sectioncorresponding to the first radial position of the optical pickup, movesthe optical pickup by a movement distance in a radial direction of theoptical disc; and a laser beam irradiation position controlling sectionwhich changes an irradiation position of the laser beam so that thelaser beam is moved along a different laser irradiation locus on theoptical disc in each rotation, whereby the density of the image issubstantially uniform.
 2. The optical disc recording apparatus accordingto claim 1, wherein the power of the laser beam is controlled by a laserpower controlling section to be substantially constant.
 3. The opticaldisc recording apparatus according to claim 1, wherein the optical discrecording apparatus forms the image on the optical disk in accordancewith image data using the optical pickup, the rotating section, thefeeding section, the detecting section and the storage section.
 4. Theoptical disc recording apparatus according to claim 1, wherein thenumber of rotations of the optical disc for respective radial positionsare set so as to be further increased as the radial position is furthermoved from an inner peripheral side of the optical disc toward an outerperipheral side of the optical disc.
 5. A method of forming an image onan optical disc comprising steps of: rotating the optical disc atsubstantially constant speed; applying a laser beam of substantiallyconstant power to the optical disc by an optical pickup; storing a tableincluding radial positions of the optical pickup and a correspondingnumber of rotations the optical disc is to be rotated for each of theradial positions, wherein the number of rotations for each of the radialpositions is different; detecting a first radial position of the opticalpickup; moving the optical pickup in a radial direction of the opticaldisc when the optical disc has been rotated the corresponding number ofrotations identified in the table for the first radial position; andchanging an irradiation position of the laser beam so that the laserbeam is moved along a different laser irradiation locus on the opticaldisc in each rotation, whereby the density of the image is substantiallyuniform.
 6. The method according to claim 5, wherein the power of thelaser beam is controlled by a laser power controlling section to besubstantially constant.
 7. The method according to claim 5, wherein thenumber of rotations of the optical disc, for respective radial positionsare set so as to be further increased as the radial position is furthermoved from an inner peripheral side of the optical disc toward an outerperipheral side of the optical disc.
 8. An optical disc including aheat-sensitive layer in which an image is formed by discoloring theheat-sensitive layer, the image being formed by the process comprisingthe steps of: rotating the optical disc at substantially constant speed;applying a laser beam of substantially constant power to the opticaldisc by an optical pickup; storing a table including radial positions ofthe optical pickup and a corresponding number of rotations the opticaldisc is to be rotated for each of the radial positions, wherein thenumber of rotations for each of the radial positions is different;detecting a first radial position of the optical pickup; moving theoptical pickup in a radial direction of the optical disc when theoptical disc has been rotated the corresponding number of rotationsidentified in the table for the first radial position; and changing anirradiation position of the laser beam so that the laser beam is movedalong a different laser irradiation locus on the optical disc in eachrotation, whereby the density of the image is substantially uniform. 9.The optical disc of claim 8, wherein the power of the laser beam iscontrolled by a laser power controlling section to be substantiallyconstant.
 10. The optical disc according to claim 8, wherein the numberof rotations of the optical disc for respective radial positions are setso as to be further increased as the radial position is further movedfrom an inner peripheral side of the optical disc toward an outerperipheral side of the optical disc.